[98] Interstellar-Gas Experiment (A0038)
Background
In the past, the observed regularities in the abundance of elements and their isotopes, upon which the theory of nucleosynthesis rests, have been obtained primarily from solar system abundances, in particular meteoritic, solar, terrestrial, and solar-wind data. However, this sample represents only a tiny fraction of the material of the universe. Thus, even a small sample of extra-solar-system isotopes will give significant insight into the various element-building processes that have occurred in the original nucleosynthesis and those which have been going on in our galaxy. Isotopic analysis of the noble-gas component of the interstellar gas will provide a significant new data source and will complement other promising techniques, such as millimeterwave, cosmic-ray, and nuclear-gamma-ray astronomy.
Objectives
The primary objective of this experiment is to collect interstellar gas atoms in metal foils at several locations around the Earth's orbit. These panicles arrive in the vicinity of the Earth as the neutral interstellar wind penetrates the heliosphere and enters the region of the inner planets. The flow pattern of the interstellar wind is controlled mainly by the gravitational attraction of the Sun, and its density is reduced through ionization by solar photons and by charge exchange with the solar-wind panicles. The flux of the interstellar atoms that survive the upstream journey in the solar wind is increased doe to gravitational focusing as they pass beyond the Sun. The angular distribution of these particles is also significantly modified in the gravitational focusing process. Thus the density and angular distribution of the interstellar gas flux vary considerably at different points in the Earth's orbit. In addition to these variations, the velocity of these particles as they impact the spacecraft changes over a wide range as the orbital motion of the Earth moves seasonally first upstream, then cross stream, and finally downstream in the interstellar wind. These seasonal variations constitute the [99] signature by which the interstellar panicles can be identified By collecting these panicles at several locations in the Earth's orbit, it will be possible not only to achieve an in situ detection of the interstellar gas for the first time, but also to study the dynamics of the interstellar wind as it flows through the heliosphere and interacts with the solar photon flux and the solar wind. In addition, because the dynamics of the interstellar wind depend on its density and velocity before entering the heliosphere, it will be possible to investigate these characteristics of the interstellar medium outside the region of the solar system.
Thus, the objectives of this experiment are to collect and isotopically analyze interstellar gas atoms around the orbit of the Earth for the purpose of obtaining new data relevant to understanding nucleosynthesis, and to study the dynamics of the interstellar wind inside the heliosphere and the isotopic composition of the interstellar medium outside the heliosphere.
Approach
The experiment hardware will act as a set of simple "cameras" with high-purity copper-beryllium collecting foils serving as the "film." (See fig. 45.) The experiment housing will mount and thermally control the foils, establish the viewing angles and viewing direction, provide baffling to reject ambient neutral panicles, provide a voltage grid to reject ionospheric charged panicles, sequence collecting foils, control exposure times, and protect the foils from contamination during the deployment and retrieval of the LDEF. After being returned to Earth, the entrapped atoms can be analyzed by mass spectroscopy to determine the relative abundance of the different isotopes of helium and neon. An attempt will also be made to detect argon. At present, the noble gases are the only species for which this method is sufficiently sensitive.
The experiment will use four trays, two 12-in. -deep peripheral trays and two 12-in.-deep end center trays, on the space-facing end of the LDEF. One of the peripheral trays will contain only one camera and the rest of the trays will contain two cameras. Power requirements will be supplied by LiSO2 batteries.
[101] A High-Resolution Study of Ultra-heavy Cosmic-Ray Nuclei (A0178)
Background
The measurement of the charge spectrum of
ultraheavy cosmic-ray nuclei is of vital importance in many areas of
astrophysics. Such measurements are relevant to the study of the
origin and age of cosmic rays, acceleration and propagation
mechanisms, the nucleosynthesis of the heavy elements in our galaxy,
and the search for superheavy nuclei (Z > 110), and may even lead
to improved nuclear mass formulas and beta decay rate formulas for
the heaviest nuclides. The central theme of this experiment is the
utilization of the LDEF's large area-time factor to obtain a large
and uniform sample of ultraheavy cosmic-ray nuclei in the region
Z
30.
Objectives
The main objective of the experiment is a
detailed study of the charge spectra of ultraheavy cosmic-ray nuclei
from zinc (Z = 30) to uranium (Z = 92) and beyond using solid-state
track detectors. Special emphasis will be placed on the relative
abundances in the region Z65, which is thought to be dominated by r-process
nucleosynthesis. Subsidiary objectives include the study of the
cosmic-ray transiron spectrum and a search for the postulated
long-lived superheavy (SH) nuclei (Z 110), such as 110SH294, in the
contemporary cosmic radiation. The motivation behind the search for
superheavy nuclei is based on predicted half-lives that are short
compared to the age of the Earth but long compared to the age of
cosmic rays. The detection of such nuclei would have far-reaching
consequences for nuclear structure theory.
The sample of ultraheavy nuclei obtained in this experiment will provide unique opportunities for many tests concerning element nucleosynthesis, cosmic-ray acceleration, and cosmic-ray propagation. For example, if the r-process domination for Z > 65 is confirmed, a reliable source spectrum will provide details of the nuclear environment, such as temperature and time [102] scale. This information will be of great importance to both astrophysics and nuclear physics.
The relative abundances of cosmic-ray nuclei in the region Z > 82 will lead to a determination of the age of cosmic rays directly from the decay of a primary component, in contrast to estimates based on, for example, Be10 or Cl36. The LDEF exposure may provide a sufficiently large sample of actinides to achieve this objective.
Injection of cosmic-ray particles into the acceleration process may depend upon atomic properties of the elements, such as the first ionization potential. This experiment will help to establish the existence of such mechanisms through their modulation of the ultraheavy charge spectrum.
The cosmic-ray charge spectrum in the region
30 
Z 65, based on the statistics available to date, appears
to be generally consistent with solar system material. The situation
is still uncertain, but it is hoped that a radical improvement will
be achieved with the LDEF exposure. For example, it is very important
to establish the roles played by the helium-burning slow
neutron-capture process in massive stars and the explosive
carbon-burning process during supernova explosions.
Since the LDEF orbit inclination is expected to be low (28°), the geomagnetic cutoff will prevent direct measurement of the ultraheavy energy spectrum. However, it is hoped that the slope of the energy spectrum can be determined from an analysis of the abundance distributions about the major axis of the LDEF (east-west effect).
To summarize, cosmic rays constitute a unique sample of material from distant parts of our galaxy which still bears the imprint of the source region. The ultraheavy cosmic-ray composition will provide a great deal of information about the evolution of matter in the universe. This question is closely related to understanding the origins of the elements in the solar system.
The experimental approach centers on the use of solid-state track detectors to identify charged cosmic-ray particles. The basic detector component is a thin sheet of polymer plastic (typically 250 µm thick). The determination of charge and velocity depends on the mechanism by which cosmic-ray nuclei that penetrate the plastic sheets produce radiation damage along the particle trajectories. After exposure and recovery, the detector sheets will be chemically processed to reveal the tracks produced by the passage of heavily ionizing particles. The effective amplification of a particle's radiation damage trail results from preferential chemical etching along its trajectory. The rate of etching is a unique function of the particle's ionization.
[103] The flux of
ultraheavy cosmic-ray nuclei is extremely small (on the order of 1
m-2 day-1). Consequently, the basic experimental approach
entails a large area-time factor exposure coupled with stability in a
general radiation environment and the ability to discriminate against
the overwhelming background of lower charge components. The main
polymer plastic used for the track detectors in this experiment will
be Lexan polycarbonate*, which has a
registration threshold given by Z/
56. It is this threshold property
that enables the Lexan to isolate individual ultraheavy nuclei in a
very high flux environment of lower charge nuclei.
A new polymer track detector, based on CR-39,
is being developed for inclusion in the LDEF experiment. Its
predominant characteristic is a very low threshold (Z/ 10) and it
potentially has very high resolving power. By using CR-39 to
complement the Lexan, it will be possible to study relativistic
nuclei in the lower charge regions, down to iron and below.
The nuclear track detectors, with lead foil energy degraders, will be assembled in stacks that will be mounted in aluminum cylinders designed to fit into 12-in.-deep peripheral trays. Three cylinders, each containing four stacks, will be placed parallel to the x-axis of each tray. (See fig. 46.) The cylinders are approximately 46 in. Iong and approximately 10 in. in diameter, and have a wall thickness of approximately 0.5 g cm2. The stacks will have a thickness of approximately 4 g/cm2 and will be mounted parallel to the tray base and placed symmetrically about the main axis of each cylinder using an Eccofoam matrix.
The trays will be thermally decoupled from the LDEF frame and will carry thermal covers flush with their outer rims. Sixteen trays will be employed. Figure 47 shows a photograph of one of the trays.
* Following the recent discovery by the Dublin group of
Tuffak polycarbonate as a track detector for heavy cosmic rays this
detector material has also been incorporated.
[105] Heavy Ions in Space (M0001)
Background
Since 1972, an anomalous flux of N, O, and Ne relative to carbon has been observed in the energy region from 3 to 100 MeV/u. Between 30 and 100 MeV/u, the abundance and energy spectrum of this flux are poorly known, and above 100 MeV/u they are completely unknown. A low-inclination orbit would be particularly suitable for studying this component because the geomagnetic field screens out the fully stripped cosmic-ray nuclei below 2250 MeV/u. Therefore, the present experiment permits a study of the newly observed nuclei in the unexplored region above 100 MeV/u, which were "covered up" by cosmic-ray nuclei in previous experiments. The source of this component is unknown but is believed to be of extrasolar origin because of the lack of a gradient away from the Sun, anticorrelation with the sunspot cycle, anticorrelation with solar (I MeV) proton flux, and a C/O ratio that is not typical of the solar abundances. It has been proposed that if the origin of this component is extrasolar, the most likely source is neutral interstellar gas that is first singly ionized by the solar wind and or solar ultraviolet radiation and then accelerated by the interplanetary solar plasma. Any knowledge of the mechanism by which this component interacts with the solar wind gives important insight into these processes and the nature of the solar plasma. A question to be explored is whether the solar plasma beyond the Earth's orbit can accelerate particles to energies greater than or equivalent to 100 MeV/o. If, on the other hand, the component is of solar origin, it would be most important to understand the production and acceleration mechanisms that are responsible.
The heavy nuclei provide a sensitive probe to test the origin of radiation belt particles. Two processes contribute to the radiation belt particles: neutron decay, and injection and local acceleration of solar-wind particles. Heavy nuclei provide a pure sample of the second type. Hence, they permit us to determine to which energies solar-wind particles can be accelerated in the Earth's field and the magneto tail, and to what extent this contributes to the radiation belt. The previous experiment on Skylab concerning heavy radiation belt nuclei did not permit a clear separation from the anomalous component. The higher geomagnetic cutoff of a low-inclination orbit would provide a clear separation of these components.
The importance of ultraheavy (UH) nuclei measurements lies in the fact [106] that these nuclei can be synthesized only in special astrophysical settings. Thus, the charge spectrum in the UH region reveals the character of the sources more directly than is possible from the charge spectrum of the lighter nuclei. In addition, the UH nuclei provide sensitive indicators of the amount of interstellar propagation and the time of travel of the galactic radiation. The problem in studying UH nuclei has been their extremely low flux. This is aggravated by their short interaction lengths, which lead to rapid absorption in even a few grams per square centimeter of atmosphere. They are best observed above the atmosphere with detectors of prodigious collecting power.
Existing data on heavy ions in space have mostly come from relatively small, electronic detectors exposed in satellites and short-duration rocket flights. This experiment will use a relatively new, independent technique (sensitive plastics) on a recoverable, long-duration exposure. This represents the first opportunity for an experiment of such large collecting power.
Objectives
This experiment will investigate three components of heavy nuclei in space: (1) a recently observed anomalous component of low-energy nuclei of N, O, and Ne; (2) the heavy nuclei in the Van Allen radiation belts; and (3) the UH nuclei (Z > 30) of the galactic radiation.
The study of the anomalous flux of N, O, and Ne nuclei in the unexplored energy region above 100 MeV/u is expected to provide new insights into the source of this component. Its observation in this experiment will confirm that these ions are singly charged.
Knowledge of the energy spectra of the heavy nuclei observed in the Van Allen belts is expected to enhance the understanding of the origin of the belts (e.g., injection and local acceleration processes). The observation of these heavy ions could show, for the first time, that low-energy particles of extraterrestrial origin can diffuse to the innermost parts of the magnetosphere. Measurements of the UH component are expected to contribute information concerning its source, interstellar propagation, and the galactic storage time.
Approach
The data will be obtained in a stack of passive particle track detectors (special etchable plastic materials) to be exposed above the Earth's atmosphere for 6 to 12 months in a low-inclination orbit, then recovered and subsequently processed under controlled laboratory conditions. Measurements will be made of the composition and energy spectra of the low-energy nuclei of N, O, and Ne and the heavy nuclei in the Van Allen radiation belts and of the charge spectrum of the UH nuclei of the galactic radiation. Each [107] detector stack has an active area of 12 in. by 14 in. Eight detector stacks are required for a collecting power of 776 m2-sr-days for a 1-year exposure. Each stack consists of two parts, one for low-energy ions and one for cosmic rays. The portion devoted to cosmic rays is in a sealed container, and the smaller portion devoted to low-energy ions is placed (in a vacuum) on top of the sealed container (fig. 48).
Radiation damage is induced in most solids
along the path of a charged particle and is a function of the primary
ionization rate. For plastic materials. after appropriate processing
(etching), the path, or "track", is visually observable (under a
microscope) as an etched cone. The different plastics have their own
threshold for track recording. These are related to the charge of the
penetrating particle; that is, for each charge (i.e., each atomic
nucleus), one can plot the primary ionization rate as a function of
velocity. Thus, for example, oxygen nuclei will not register in a
Lexan detector until they have slowed down to 0.12, after which the remainder of
the track will be etchable. The detector must then be designed to
bring oxygen nuclei to rest with a minimum probability of nuclear
interaction. UH nuclei will leave etchable tracks over a much larger
fraction of their range.
The thickness of the detector is approximately 10 g/cm2. This is necessary to bring to rest oxygen nuclei up to approximately 240 MeV/u. The stacks consist of sheets of track-detecting plastic. Lexan will be used for the low-energy stacks, and the cosmic-ray stacks will consist primarily of CR-39. The detector stacks are completely passive; even temperature and pressure are [108] monitored by passive techniques. After recovery, processing and track measurements will be done at the Naval Research Laboratory.
Charge estimates are based on etch cone
measurements. (The etching rate is calibrated as a function of the
ionization density.) The charge resolution achievable with CR-39 is
approximately 0.35 for nuclei at Z 26. Calibrations will be carried
out with laboratory beams of heavy ions.
It is apparent from existing measurements of the energy spectra of the various components at an orbit of 28° and from those outside the magnetosphere that if the anomalous component is observable (at the 28° orbit), then it should be clearly resolved from both the radiation belt and the galactic nuclei at kinetic energies of 100 to 200 MeV/u.
[109] Trapped-Proton Energy Spectrum Determination (M0002-1)
Background
The purpose of this experiment is to quantify the flux of ions with energies greater than I MeV. The main experiment is sponsored by the Air Force Geophysics Laboratory for the purpose of measuring the energetic protons trapped in the Earth's magnetic field. A series of subexperiments are included which have different but related goals.
Objective
The objective of this experiment is to measure the flux and energy spectrum of protons with energies of I to 10 MeV. These protons are trapped on the Earth's magnetic field lines as part of the inner radiation belt, or Van Allen zone. The proton will be encountered predominantly in the South Atlantic anomaly at a 90° pitch angle.
The experiment consists of 18 stacks of passive plastic detectors (CR-39) arranged in portions of three LDEF trays. (See fig. 49.) The stacks are 1.49...
[111] ....in. square and 2.60 in. high. They are mounted in containers on a plate arranged in the trays to be normal to the Earth's magnetic field in the South Atlantic anomaly (SAA). The bottom half of each stack is composed of CR-39 without DOP and is 0.022 in. thick. The next 40 percent of the stack is CR-39 with DOP and is 0.022 in. thick. The top 10 percent of the stack is CR-39 with CHPC and is 0.011 in. thick. The stack is open to the vacuum of space. The top layer of plastic is directly exposed to space. A sheet of aluminum 0.001 in. thick separates each layer of plastic. Five of each six stacks are perpendicular to the magnetic field in the South Atlantic anomaly.
The three stacks of metal squares and the microsphere container which are visible in figure 49 are used in the three subexperiments described here.
Neutron and Proton Activation on LDEF (NASA Marshall Space Flight Center and Eastern Kentucky University)
Radioactivity induced by protons and neutrons in the LDEF orbit will be determined by exposing metal samples to the ambient flux through the mission duration and measuring resulting gamma ray activation spectra in a low-level counting facility after recovery. In low Earth orbit, the main sources of activation will be primary cosmic rays, SAA protons, secondary neutrons, and atmospheric albedo neutrons. Induced radioactivity will be a major source of background radiation for certain classes of Shuttle-launched experiments. A quantitative determination of this activation during an early Shuttle mission is important to assess this source of background radiation. The metal samples that were chosen for flight have unique nuclear properties that make them suitable for these activation studies. One property is the relatively high probability that the sample will become radioactive following the passage of a neutron or proton. In addition, the sample will retain a measurable amount of radioactivity upon its return.
Microsphere Dosimetry (Clarkson College of Technology)
Containers of small microspheres flown on LDEF will be used to record the energy deposited in volume elements with microscopic dimensions as a result of exposure to the natural radiation environment of space. The single event-upset phenomena and hard errors in microelectronics, as well as the radiobiological effects in man, result from ionizations generated within sensitive volumes that have microscopic dimensions. Standard dosimetry measurements of the radiation environment of space are carried out using macroscopic sensitive volumes. Even a relatively small macroscopic dose can include order-of-magnitude differences in the number of ionizations in microscopic volume elements. Microspheres of different composition and diameter will be flown under identical conditions. Thermoluminescent dosimeters (TLD's) will be included to measure the macroscopic dose received [111] by each sample. Physical properties of the microspheres, such as changes in diameter after a period of postflight etching, will be measured to determine the dose received by each microsphere.
Flux Measurement by lon Trapping (Army Materials and Mechanics Research Center)
Concentration profiles will be measured, primarily by secondary ion mass spectroscopy and Rutherford backscattering, for a wide variety of ions at different places on a series of metal plates directly exposed to space. The area under a profile and the profile shape give the total flux and energy distribution information. Sample materials include fused quartz (SiO2), aluminum oxide (Al2O3), aluminum, copper, silicon, tantalum, tungsten, and zirconium.
[112] Measurement of Heavy Cosmic-Ray Nuclei on LDEF (M0002-2)
Background
The long-duration flight on LDEF will provide the opportunity to collect a reasonable number of heavy cosmic-ray nuclei. A knowledge of the abundance of these nuclei is essential to any theory on the source, acceleration, propagation, confinement, and age of cosmic rays.
Objective
The objective of this experiment is to measure the elemental and isotopic abundances of heavy cosmic-ray nuclei with nuclear charge Z equal to or greater than 3. The chemical and energy spectra will be measured for particles that have energies in the range from 20 to 1000 MeV per atomic mass unit. Two points of great interest are "geomagnetically forbidden" cosmic-ray particles and heavy ions of the trapped radiation.
Approach
The experiment is passive and occupies one-sixth of a 3-in.-deep peripheral tray with several other experiments. The experiment package consists of visual track detectors that remain sensitive throughout the LDEF mission. (See fig. 50. ) The scientific data are stored in latent tracks and can be revealed in the investigator's laboratory after recovery.
The detector stack consists of approximately 6.5 g/cm2 of CR-39 plastic visual track detector sheets that have a well-established response. The detector stack is housed in an aluminum container that provides structural support and thermal contact to the LDEF structure. The top of the detector stack is covered by thin coated foils that provide thermal shielding and decoupling from deep space.
Heavy ions stopping in or passing through the plastic sheets of the stack produce latent tracks that can be revealed by chemical etching in the laboratory. Further analysis can be performed under optical and electron microscopes by measuring the shape and length of the etched cones. These parameters depend strongly on the energy loss along the trajectory of the incoming particle. The determination of nuclear charge and mass is based on the cone length versus residual range method. Plastic track detectors have registration [114] thresholds that make the detector system almost insensitive to electrons and protons except at low energies; therefore, they do not produce a disturbing background.
[115] Linear Energy Transfer Spectrum Measurement Experiment (P0006)
Background
The linear energy transfer (LET) is the energy deposited per unit path length of a charged particle traversing matter. For estimating the rate of damage from single-hit phenomena, the quantity that best combines the radiation environment, orbital situation, and spacecraft shielding is the linear energy transfer (LET) spectrum at the device location. To date, LET spectra measurements have been severely limited by statistics due to the short nature of STS missions. The designers of future long-life spacecraft such as a space station need LET spectra measurements for exposures of I year or more to establish shielding requirements and to select materials and devices that will not be adversely affected in space during the required operation life.
Objectives
This experiment will measure the LET spectrum behind different shielding configurations for approximately 1 year. The shielding will be increased in increments of approximately 1 g/cm2 up to a maximum shielding of 16 g/cm2. In addition to providing critical information to future spacecraft designers, these measurements will also provide data that will be extremely valuable to other experiments on LDEF.
Approach
A combination of thermal luminescence and track type detectors will be used to measure the LET. Aluminum will be used for the shielding. The passive detectors and shielding material will be placed in the canister shown in figure 51. The canister with detectors will be sealed with approximately I atm internal pressure. Control detectors identical to those to be flown will be used to establish the terrestrial background radiation to which the flight detectors are exposed prior to launch and after recovery.
[117] Multiple-Foil Microabrasion Package (A0023)
Background
A number of the early Explorer satellites, the Ariel II, and three Pegasus satellites measured meteoroid penetrations in near-Earth space. These inspace penetration measurements, in addition to providing spacecraft design data, were used with existing ground-based radar and visual meteor data to extend size estimates of the near-Earth meteoroid environment to particles as small as approximately 10-10g.
Other early U. S. and Russian spacecraft used microphone type meteoroid detectors to measure small-particle impact fluxes. The microphone data indicated a small-particle population much greater than that indicated by the penetration measurements. The microphone data were, in fact, interpreted by some to indicate a dust belt around the Earth.
Difficulties in simulating meteoroid impacts in the laboratory created a number of uncertainties in interpreting both the microphone and penetration early measurements in terms of the near-Earth meteoroid environment.
Data on the near-Earth meteoroid environment have also resulted from analysis of the lunar-material samples obtained during the Apollo Program. The analysis of craters on the lunar material in terms of the meteoroid environment is limited by the facts that the craters occurred over a very long period of time (105 to 106 years) and the exact exposure time is uncertain.
Taking advantage of the now recoverable and improved very sensitive thin-foil penetration detectors, this experiment will make a substantial step toward the elimination of a number of the remaining uncertainties in the estimates of the near-Earth micrometeoroid environment. In a very cost-effective way, the experiment will provide both design data regarding the erosion of spacecraft by microparticles and data on the near-Earth micrometeoroid environment.
Objectives
The specific scientific objectives of this experiment are to measure the spatial distribution, size, velocity, radiance, and composition of microparticles in near-Earth space. The technological objectives are to measure erosion rates resulting from microparticle impacts and to evaluate thin-foil [118] meteor "bumpers." The combinations of sensitivity and reliability in this experiment will provide up to 1000 impacts per month for laboratory analysis and will extend current sensitivity limits by 5 orders of magnitude in mass.
Approach
The experiment approach utilizes the well-established technique of thin-foil hypervelocity penetration supported by extensive investigations and calibrated in laboratory simulation to a high precision. Several of the different classes of impact events anticipated on encounter with such a thin-foil array are illustrated in figure 52. This range of classes indicates the potency of this technique compared to simple polished plates or single-foil penetrations. Deployment of such thin-foil detectors around LDEF will measure the spatial anisotropy of the impact flux. Microprobe analysis of penetration and spallation areas after recovery will determine the particle elemental composition.
The detector design utilizes rolled aluminum foil down to a thickness of 1.5 µm (fig. 53). Bonding to etched grid supports achieves very rugged structures capable of withstanding vibrational levels and atmospheric pressure gradients typical of the LDEF-Shuttle environment.
The experiment will be located in one-third of each of four 3-in.-deep trays located at 90° intervals around the LDEF periphery and in about two-thirds of a 3-in.-deep end corner tray on the space-facing end of the LDEF.
[121] Study of Meteoroid Impact Craters on Various Materials (A0138-1)
Background
Interplanetary dust particles (micrometeoroids) are expected to form well-defined craters upon impacting exposed material in space. Studying the frequency and features of these craters will provide data on the mass-flux distribution of micrometeoroids and, to a lesser extent, on the velocity magnitude and direction. Limited crater studies have been done in the past with materials retrieved after exposure in space on Surveyor 3, Apollo 4 and 11, Gemini 10 and 11, and Skylab. However, little has been learned regarding the composition of impacting particles. This experiment will focus on the determination of the composition of meteoroid material residues inside craters.
Objectives
This experiment will study impact craters produced by micrometeoroids on selected materials (metals and glasses in the form of thick targets) to obtain valuable technological and scientific data. Specifically, the studies will focus on determining micrometeoroid composition and mass-flux distribution. Analyses will also be made on the distribution of impact velocity vectors.
Approach
High-velocity impact effects on various materials have been studied extensively in the laboratory. It is, however, impossible to obtain velocities higher than 7 to 8 km sec with relatively large particles (> 10-9 g). The LDEF can provide a unique opportunity to expose large-area targets for an extensive period of time and to recover them for subsequent analysis. Selected materials that act as impact detectors will be exposed to space. This method is entirely passive and consists of thick targets (compared to the dimensions of expected particles) of pure metals and glass. The collecting area ( ~750 cm2) is expected to record, with a high probability, impacts of micrometeoroids with a mass in the range of 10-14 to 10-17 g (corresponding to 0.2- to 35 µmparticle diameters). The experiment is accommodated on an aluminum mounting plate (420 by 400 mm) located in one-sixth of a 12-in.-deep peripheral tray that contains nine other experiments from France. (See figs. 12 and 54. ) Two types of samples will be used (table 12). Type I will be metallic surfaces (100 [122] by 100 mm) bolted to an aluminum mounting plate (6 samples). Type 11 will be glass samples (25 mm in diameter) bolted to an aluminum mounting plate (27 samples). A set of similar samples will remain in the laboratory for subsequent comparison with space-exposed samples. A set of samples will also be retained to perform tests with a hypervelocity accelerator.
The first task after experiment retrieval will be a careful scanning of exposed material to search for impact microcraters. Usually, high-velocity craters produced in metals and in brittle materials have a distinctive mor-....
[123] ....-phology and can be distinguished easily from other surface features. An optical microscope will be used to identify craters larger than about 10 µm, and such a crater is expected every 2 to 3 cm2. The density of micrometersized craters will be higher (1 to 10 per cm2), but the necessary use of a scanning electron microscope (SEM) with 1000x magnification will limit the area to be scanned. (See table 13.)
Measurements made on craters will include diameter and depth measurements that, by comparison with experimental results, will give the mass and density of impacting particles. Velocity can be estimated from the morphology of craters produced on brittle materials. Impact direction can be evaluated by the shape of the craters. There is a close relationship between the circularity of craters and the angle of impact. The relationship between flux and mass will be derived from the areal density of microcraters.
For craters showing evidence of remnants of the projectile, chemical analysis will be made with X-ray microprobe and ion or Auger microprobe. If possible, atomic absorption spectrophotometry or neutron activation analysis will also be used.
|
Sample |
|
|
|
|
. | |||
|
A1 |
Tungsten |
150 |
100x100 |
|
A2 |
Aluminum |
250 |
100x100 |
|
A3 |
Copper |
125 |
100x100 |
|
A4 |
Stainless steel |
250 |
100x100 |
|
A5 |
Aluminum |
250 |
100x100 |
|
A6 |
Stainless steel |
250 |
100x100 |
|
B1 to B27 |
Pyrex glass |
1.9 |
25 (diam.) |
|
Instrument |
|
|
|
|
|
|
. | |||||
|
Optical microscope |
20x |
25 - 40 |
10-9 |
400 |
60 |
|
40x |
10 - 20 |
10-10 |
80 |
17 | |
|
80x |
5 - 10 |
10-11 |
20 |
8 | |
|
SEM |
100x |
5 - 10 |
10-11 |
4 |
2 |
|
300x |
2 - 3 |
10-12 |
1.4 |
1 | |
|
1000x |
1 - 2 |
10-13 |
0.06 |
1 | |
|
5000x |
0.2- 0.5 |
10-14 |
0.006 |
1 | |
a About 250 hours of SEM scanning time are expected.
[124] Attempt at Dust Debris Collection With Stacked Detectors (A0138-2)
Background
Since the beginning of space exploration, a significant amount of data has been gathered on micrometeoroids. Flux-mass relationships, velocities, and orbits of the particles have been established with meteoroid impact and penetration detectors on satellites and space probes. Also, studies of impact craters on lunar samples and a few retrieved sample materials exposed to space have added data on micrometeoroids. However, these techniques have limitations that prevent the study of undisturbed particles.
To study undisturbed particles, cosmic-dust collectors have been flown on balloons and rockets, and more recently on high-altitude aircraft. These techniques for dust collection in the atmosphere are limited because of short exposure times and uncertainty in the discrimination between cosmic-dust particles and terrestrial contaminants.
Objective
The primary objective of this experiment is to investigate the feasibility of future missions of multilayer thin-film detectors acting as energy sorters to collect micrometeoroids, if not in their original shape, at least as fragments suitable for chemical analysis. It is expected that this kind of particle collector will help in solving one of the most puzzling topics in cosmic-dust studies: the mineralogical and chemical composition of the particles. This is a matter of great interest in the study of the origin and evolution of the solar system.
Approach
The experiment will consist of targets made of one or two thin metal foils placed in front of a thicker plate. The maximum sample thickness of 125 µm has been chosen to prevent foil perforation by particles with a mass in the range of 10-8 g. A particle penetrating the foil undergoes either a deceleration or a fragmentation, according to the thickness and nature of the foil. Thicknesses chosen for this experiment range from 0.75 to 5 µm of aluminum and are expected to slow down particles with diameters between I and 10 µm without complete destruction.
[125] The experiment will include 31 samples with a sampling surface area of 240 cm2 The samples will be mounted on a plate inside one of the FRECOPA boxes in a 12-in. -deep tray that contains nine other experiments from France. (See figs. 12 and 13.) The FRECOPA box will provide protection for the fragile thin metal films before and after space exposure. The description and list of samples are given in table 14. All samples will be mounted within aluminum frames (40 by 40 mm or 30 by 30 mm) which will hold the thick target and the thin foils in front. (See fig. 55.)
Measurements after flight exposure will be similar to those described for experiment A0138-1. Emphasis will be on the study of thin-film behavior during the cratering process and on the chemical analysis of projectile remnants.
|
Sample |
|
|
|
|
. | |||
|
D1 to D6 |
Aluminum |
|
|
|
Aluminum |
|
| |
|
D7, D8 |
Aluminum |
|
|
|
Aluminum |
|
| |
|
Aluminum |
|
| |
|
D9, D10, D11 |
Aluminum |
|
|
|
Aluminum |
|
| |
|
D12 |
Aluminum |
|
|
|
E1 to E6 |
Aluminum |
|
|
|
Gold |
|
| |
|
E7, E8, E9 |
Aluminum |
|
|
|
Aluminum |
|
| |
|
E10, E11, E12 |
Aluminum |
|
|
|
Gold |
|
| |
|
E13 to E16 |
Gold |
|
|
|
E17 |
Aluminum |
|
|
|
Aluminum |
|
| |
|
Aluminum |
|
| |
|
E18 |
Aluminum |
|
|
|
Gold |
|
| |
|
Aluminum |
|
| |
|
E19 |
Aluminum |
|
|
[127] The Chemistry of Micrometeoroids (A0187-1)
Background
The mineralogy, petrography, and chemistry of both "primitive" and more evolved meteorites recovered on Earth are currently the subjects of intense laboratory studies. The purpose of these studies, in conjunction with our knowledge of terrestrial and lunar petrogenesis, is to establish an observational framework that can be used progressively to constrain and refine cosmochemical and mechanical-dynamic models of early solar-system evolutionary processes. Such modelling attempts include the nature and kinetics of nebular condensation and fractionation, the accretion of solid matter into planets, the differentiation and crustal evolution of planets, and the role of collisional processes in planetary formation and surface evolution. All of these processes are known to be highly complex.
Fine-grained interplanetary particles (micrometeoroids) of masses as little as 10-16 g are, however, largely excluded from models of the early solar-system evolution because their mineralogic, petrographic, and geochemical nature is largely unknown. In comparison, however, their dynamics, orbital parameters, and total flux are reasonably well established, although still fragmentary in a quantitative sense. According to current (largely dynamical) hypotheses, a majority of these objects are derived from comets. This association affords a unique opportunity to study early solar system processes at relatively large radial distances from the Sun (greater than approximately 20 AU). These cometary solids may reflect pressure and temperature conditions in the solar nebula which are not represented by any of the presently known meteorite classes, and therefore may offer potential insight into the formation of comets themselves.
[128] Objectives
The prime objective of this experiment is to obtain chemical analyses of a statistically significant number of micrometeoroids. These data will then be compared with the chemical composition of meteorites. Secondary objectives of the experiment relate to density, shape, mass frequency, and absolute flux of micrometeoroids as deduced from detailed crater geometries (depth, diameter, and plane shape) and number of total events observed.
Approach
This experiment is designed to collect micrometeoroid residue in and around micrometeoroid impact craters that are produced by hypervelocity collisions of the natural particles with high-purity targets. After the return of these targets, the micrometeoroid residue will be chemically analyzed with a large array of state-of-the-art micro analytical tools (e.g., electron microprobe, scanning electron microscope with energy-dispersive analyser, Auger and ESCA spectroscopy, and ion probe mass analyzer). in favorable cases, precision mass spectrometry may be possible. The experiment will involve both active and passive collection units.
The principles of the " active " unit are described below. (See fig. 56. ) A clam shell concept allows two sets of clam shells, housed in a 12-in.-deep....
[129] .....peripheral tray, to be opened and closed. The figure shows one set of clam shells in the stowed (i.e., closed) mode and the other set in a deployed mode. Due to the high sensitivity of the microanalytical tools and the extremely small masses of micrometeoroid residue to be analysed (10-7 to 10-12 g), the stowed configuration will protect the collector surfaces from particulate contaminants during ground handling, launch, and LDEF deployment and retrieval sequences. The clam shells will be opened by a timed sequencer some 8 days after LDEF deployment and they will close at a similar time prior to redocking for retrieval of LDEF. The basic contamination barrier is a precision labyrinth seal.
The main collector surfaces are made of 99.99-percent-pure gold sheets 0.5 mm thick and totaling some 0.85 m2 total surface area. Two individual gold panels, each about 57 by 20.6 cm, will be fastened to each clam shell tray for a total of seven panels. A high-quality surface finish will be obtained by polishing, acid etching, and electroplating. The space for the eighth panel is taken up by a series of experimental collector materials (about 6.5 by 20.6 by 0.05 cm each) for the purpose of empirically determining collection efficiency and/or optimum chemical background (i.e., signal-to-noise ratio during the analytical phase). These auxiliary surfaces consist of Al (99.999 percent pure), Ti (99.9 percent pure), Be (99.9 percent pure), Zr (99.8 percent pure), C (99.999 percent pure), Kapton (a polyimide), and Teflon filters. There are three reasons for selecting gold as the main collector surface. First, its behavior under hypervelocity impact conditions is reasonably well known, in contrast to that of some of the auxiliary surfaces. Second, gold is not an overly abundant constituent in meteorites, and third, it is a highly suitable substrate for many of the microanalytical techniques contemplated. For a model exposure duration of 9 months, a fairly well established mass frequency distribution, and a conservatively low flux estimate for micrometeoroids, the approximate numbers of micrometeorite craters expected on the gold collector are as follows: 165 craters larger than 5 µm, 52 craters larger than 10 µm, and 9 craters larger than 50 µm in diameter. Quantitative analysis is feasible only for craters larger than 20 µm in diameter (approximately 20 events), although an attempt will be made at qualitative analysis of smaller craters.
The experiment will use a "passive" collector unit that occupies a 3-in.-deep peripheral tray. (See fig. 57.) This unit will be covered by six Al (99.9 percent pure) panels (47 by 41 by 0.3 cm each). These surfaces have no special protection against contamination because they are rigidly bolted onto a structural framework which in turn is fastened to the LDEF tray. If contamination is not too significant, approximately another 25 events larger than 20 µm in diameter will be available for analysis. Furthermore, an [130] additional gold surface (approximately 12 by 2.3 by 0.05 cm) will be flown inside the experiment exposure control canister used in LDEF experiment SOO10 (Exposure of Spacecraft Coatings) for optimum calibration of gaseous and particulate contamination.
[131] Chemical and Isotopic Measurements of Micrometeoroids by Secondary Ion Mass Spectrometry (A0187-2)
Background
In the past, the study of interplanetary dust particles has been restricted mainly to measurements of their flux, mass and velocity distribution, and variation with direction and solar distance. Chemical and isotopic compositional information could be obtained from the Brownlee particles collected in the upper atmosphere. The launch of LDEF provides the first opportunity to collect micrometeoroid material in space which then can be subjected to isotopic analysis in the laboratory. Isotopic measurements of interplanetary dust are of great interest since at least part of the interplanetary dust is believed to be derived from comets. Because comets originate in the outer region of the solar system they probably have never been subjected to mixing of material during formation of the solar system, and thus they might have preserved presolar isotopic features.
Interplanetary dust particles are difficult to collect because of their high speed. Upon impact, much of the particle mass is evaporated and ejected from the target. This experiment utilizes a target covered with a thin foil to trap the elected material.
[132] Objective
The objective of this experiment is to measure the chemical and isotopic composition of interplanetary dust particles of mass greater than 10-10 g for most of the major elements expected to be present.
Approach
The experiment approach utilizes a passive Ge target which is covered with a thin metallized plastic foil. The foil is coated on the outer (i.e., space facing) surface with a Au-Pd film for thermal control and to protect the foil from erosion by atomic oxygen present in the residual atmosphere. The inner surface of the foil is coated with tantalum, which was selected in order to optimize the analysis of positive secondary ions by secondary ion mass spectroscopy (SIMS).
The experiment occupies a 3-in.-deep peripheral tray near the LDEF leading edge, one-third of a 6-in. -deep peripheral tray near the LDEF trailing edge, and two-thirds of a 6-in.-deep peripheral tray on the LDEF trailing edge. Figure 58 shows the one-third-tray experiment hardware and illustrates the micrometeoroid detection principle. An incoming meteoroid penetrates the foil before striking the target plate. Impact ejecta, consisting of a mixture of target and projectile material in the form of fragments, melt, and vapor, are collected on the underside of the film. The deposited interplanetary dust material can be analyzed by a number of surface-sensitive techniques, among which SIMS is favored because of its high sensitivity and its isotopic analysis capability. Measurements are planned of the concentrations of Na, Mg, Al, Si, S, K, Ca, Fe, and Ni and the isotopic compositions of Mg, Si, Ca. and Fe (and possibly S and Ni) from particles greater than 10 µm in diameter. For an exposure of 12 months, approximately 60 impacts of particles of this size are expected for an area of 1 m2. About 1 m2 will be exposed on both the leading and the trailing edge. The leading edge has the advantage of receiving a higher flux because of the higher impact velocity (approximately 20 km/sec). On the trailing edge, impacts from terrestrial contaminants in orbit are excluded. In addition to chemical and isotopic measurements, information on particle mass, velocity, and density can be obtained from the study of the hole size and crater size and morphology.
[134] Interplanetary Dust Experiment (A0201)
Background
The study of interplanetary dust historically has been plagued by the problem of low data rates and therefore statistically inadequate data analyses. The LDEF satellite will permit for the first time the flight of an experiment with a large effective area, yielding data with which excellent statistical confidence can be achieved. Additionally, it has been shown that a major I source of the interplanetary micrometeoroid environment is comets. Confirmation and expansion of these results may give important insight into the cometary phenomenon.
Objectives
The objective of this experiment is to study interplanetary dust, variously referred to as cosmic dust, cometary dust, zodiacal dust, or meteoric dust particles. Specific objectives are to obtain information regarding particle mass and velocity, and to undertake correlative analyses with other experiments, both on LDEF or near the time of the LDEF flight.
Approach
The experiment will use metal-oxide-silicon (MOS) capacitor-type impact sensors with two different sensitivities. The total active area of the experiment will be about 1 m2. Sixty percent of the sensors will have an oxide thickness of 0.4 µm, the higher sensitivity, and 40 percent will have a thickness of 1.0 µm.
The experiment will be located in four locations spaced at 90° intervals around the LDEF periphery and on the Earth-facing and space-facing ends. (See fig. 59.) Tray requirements include one 6-in.-deep tray, one-third each of three 3-in.-deep trays, one 3-in.-deep end corner tray on the Earth-facing [135] end, and about one-third of a 3-in -deep end corner tray on the space-facing end. A one-third-tray location typically will contain 80 impact sensors and 1 Sun sensor.
Approximately every 2 hours, an experiment power and data system will record the status of all sensors and the recent experiment activity, which will include the time of occurrence of each impact and the total number of impacts for each sensitivity and tray location. The Sun sensors will be used to record the time from the most recent crossing of the dark-to-light terminator.
When the experiment is recovered, the recorded data and LDEF tracking data will be analyzed to determine the dust encountered as a function of mass, time, and velocity direction in geocentric coordinates. These data will then be correlated with theories and observations of other dust-related phenomena.
[136] Space Debris Impact Experiment (S0001)
Background
Current models of the near-Earth meteoroid environment are based on measurements by many different types of detectors, each measuring over its own narrow mass range with no overlapping of measurements. None of the detectors measures mass or size directly. As a consequence, an uncertain fitting together of the data has been used to estimate the population and size distribution of meteoroids near the Earth. This experiment will use the same detector, an aluminum plate, to detect meteoroids over a very large size range. A single factor that converts crater size to meteoroid mass can be applied to all the data. A much improved population and size distribution of meteoroids will be obtained.
Man-made debris may someday become a significant component of the space debris environment near the Earth. Future spacecraft explosions, whether accidental or intentional, can result in millions of fragments, each capable of inflicting substantial impact damage. Such fragments could remain in orbit for years. An estimate of the current man-made debris population will also be made with the experiment.
Objectives
The specific objectives of this experiment are to establish the population and size distribution of meteoroids in the mass range from 10-10 to 10-4 g, to establish the current population of man-made debris in the same mass range, and to obtain data on the physical properties (composition and density) of meteoroids.
Approach
The space debris impact experiment will expose large areas of thick aluminum plates to the space debris environment. The size distribution of the craters caused by meteoroids will be used to determine the population and size distribution of meteoroids. The size distribution of craters caused by manmade debris will be used to determine the population and size distribution of man-man debris. The shape of the craters, the impacting particle material found on the crater walls, and the location of the impacts on the spacecraft will [137] be used to distinguish between meteoroid craters and those caused by man-made debris.
This experiment occupies 19 3-in.-deep peripheral trays, two 3-in.deep end corner trays on the Earth-facing end, and one 3-in.-deep end corner tray on the space-facing end of the LDEF. Additionally, several partial tray locations on the periphery will be utilized.
[138] Meteoroid Damage to Spacecraft (P0007)
Consortium of investigators*
Background
Observation of meteoroid impact damage to typical spacecraft components (i.e., solar cells, thermal control surfaces, and composite materials) can provide valuable information for the design of future spacecraft. A detailed inspection of LDEF and the LDEF experiments will probably reveal a number of examples of such damage. The LDEF will be the first large spacecraft to be exposed in space for an extended period of time and then recovered in such a manner that the external surfaces are not damaged by the recovery process. In addition, the experiments in the LDEF trays will expose examples of many typical spacecraft components to the space environment.
Objective
The objective of this experiment is to obtain examples of meteoroid impact damage to typical spacecraft components, and by so doing to help establish design approaches to minimize meteoroid damage effects to future spacecraft. The results of the complete inspection of the LDEF will complement and extend the data obtained from specific meteoroid experiments flying in LDEF trays.
Approach
All exposed external surfaces of LDEF and the experiments will be examined after retrieval before any experiment tray removal operations are begun. The locations of impact craters will be documented and the principal investigators of the trays containing impact craters will be requested to make the component containing the crater available to the consortium for study after evaluation of the item has been completed.
*Consortium members will be the
investigators involved in the following meteoroid experiments: A0023,
Multiple-Foil Microabrasion Package; A0138-1, Study of Meteoroid
Impact Craters on Various Materials: A0138-2, Attempt at Dust Debris
Collection With Stacked Detectors; A187-1, The Chemistry of
Micrometeoroids: A0187-2, Chemical and Isotopic Measurements of
Micrometeoroids by Secondary lon Mass Spectrometry; A0201,
Interplanetary Dust Experiment; and S0001, Space Debris Impact
Experiment.
[139] Free-Flyer Biostack Experiment (A0015)
Background
Studies on the biological effectiveness of HZE particles (particles of high atomic number Z and high energy) and stars are necessary to confirm ground-based work, as well as to assess the biological effects of HZE particles not currently available from accelerators on Earth. Spaceflight experiments are required to analyze and evaluate the biological effects of the different species of HZE particles prevalent in space.
In comparison with the Apollo lunar mission, the dosimetric data calculated for a 6-month flight of LDEF will yield an increase in total dose of approximately 360 percent, in HZE particle fluence of approximately 200 percent. and in stars of even 2700 percent. Thus LDEF will offer a unique opportunity to gather information on the effects of stars on biological matter.
Objectives
The free-flyer biostack experiment is part of a radiobiologicai space research program that includes experiments in space as well as in accelerators on Earth. The program has been specially designed to increase knowledge concerning the importance, effectiveness, and hazards of the structured components of cosmic radiation to man and to any biological specimen in space. Up to now, our understanding of the ways in which HZE particles might affect biological matter is based on a few spaceflight experiments from the last Apollo missions (Biostack I and II, Biocore, and Apollo light flash investigations) and the Apollo Soyuz Test Project (Biostack III). and on the limited data available from heavy-ion irradiation from accelerators. In the near future, accelerators capable of accelerating particles up to higher atomic numbers and higher energies will promote increased activity in ground-based studies on biological effects of HZE particles. Comparison of data from such irradiation experiments on Earth with those from an actual spaceflight experiment will show any potential influence of the inevitably attendant spaceflight factors (e.g., weightlessness) on the radiobiological events. Further, the long duration of the LDEF flight will increase the chance of studying the biological effectiveness even of rare components of cosmic radiation, such as iron nuclei or superheavy particles of high energy, which are not yet available from ground-based facilities.
[140] Approach
The flight hardware used to achieve this objective consists of biological specimens and nuclear track detectors. Correlation of the biological and physical events was achieved by using a special sandwich construction of visual track detectors and monolayers of biological objects. Figure 60 shows a photograph of the experiment hardware and illustrates the detector unit construction.
The fluence of heavy particles and/or nuclear disintegration stars depends on the locations of the experiment on LDEF. Therefore, two experiment locations with different shielding against space are used. The experiment consists of 20 detector units, 12 units mounted in a 6-in.-deep end corner tray on the Earth-facing end of LDEF, and 8 mounted in one-third of a 6-in.-deep peripheral tray. Each unit weighs approximately 2 kg and does not require power. Knowledge of the temperature history around the single units is necessary. For all other orbital parameters needed for the experiment, normal tracking of the spacecraft will be sufficient. All experiment data analysis will be conducted at various experimenters' laboratories in Europe and the U.S. (See tables 15 and 16.)
|
Biological object |
|
|
|
|
|
|
. | |||||
|
Biomolecules |
Rhodopsin |
CN |
Influence on the optical absorption |
S.L. Bonting |
University of Nijmegen, The Netherlands |
|
Unicellular |
Bacillus subtilis spores |
CN, Lexan, AgCI |
Influence on spore outgrowth, cell development, colony formation |
R. Facius, G. Horneck, G. Reitz, M. Schafer, J.-U. Schott, K. Baltschukat |
DFVLR, FRG |
|
Plant |
Arabidopsis thaliana seeds |
CN, Lexan, AgCI |
Influence on germination, plant development, mutation induction |
A. R. Kranz |
University of Frankfurt, FRG |
|
Plant |
Sordaria fimicola ascospores |
CN, Lexan, AgCI |
Influence on germination, mycel growth, reproduction, mutation rate |
J.-U. Schott |
DFVLR, FRG |
|
Plant |
Nicotiana tabaccum seeds |
CN |
Influence on germination, growth and development, mutation induction |
M. Delpoux
|
University of Toulouse, France |
|
Plant |
Zea mays seeds |
CN, Lexan |
Influence on germination growth, differentiation and morphogenesis, mutation induction |
C. A. Tobias, T. Yang, M. Freeling |
University of California, Berkeley |
|
Plant |
Rice seeds |
CN |
Influence on germination, growth and development, mutation induction |
M. Bayonove |
University of Monpellier, France |
|
Animal |
Artemia salina cysts |
CN |
Influence on early steps of development, metabolism (biochemical analysis), integrity of ultrastructure |
G. Gasset, Y. Gaubin, H. Planel |
University of Toulouse, France |
|
Animal |
Artemia salina cysts |
CN |
Influence on hatching, induction of development anomalies, histological anomalies |
E. H. Graul, W. Ruther |
University of Marburg, FRG |
|
Cosmic radiation component |
|
|
|
|
|
|
|
|
|
. | ||||||||
|
Heavy ions |
Nuclear emulsion |
Very broad |
No |
No |
High |
No |
H. Francois R. Pfohl, G. Heilmann |
CEA, France Centre Nucléaire Strasbourg France |
|
Heavy ions |
Plastics: cellulosenitrate polycarbonate, CR-39 |
Medium |
Yes |
Yes |
Low |
No |
O. C. Allkofer, R. Beaujean, W. Enge, G. Sermund |
University of Kiel, FRG
|
|
W. Heinrich |
University of Siegen, FRG | |||||||
|
R. Facius, G. Reitz, M. Schafer |
DFVLR, FR
| |||||||
|
M. Debeauvais, R. Pfohl |
Centre Nucleaire Strasbourg, France | |||||||
|
E. V. Benton |
University of San Francisco | |||||||
|
Heavy ions |
AgCI crystals |
Broad |
Yes |
No |
Medium to low |
Yes |
E. Schopper |
University of Frankfurt, FRG |
|
J.-U. Schott |
DFVLR, FRG | |||||||
|
Gamma rays, Xrays, protons |
LiF thermoluminescence dosimeter |
Integrating dosimeter |
. |
. |
. |
No |
G. Portal, H. Francois |
CEA, France |
[146] Seeds in Space Experiment (P0004-1)
Background
Man, when exploring and developing terrestrial frontiers, has generally carried seed for crops to support his survival. In the foreseeable future, man will probably also transport seed in space as he explores and develops that new frontier. The space environment can be hostile to seed; therefore, data are needed on the effects of space on seed and on how seed should be packaged to survive in space. As a first step toward meeting this need, the George W. Park Seed Company, inc., flew a Getaway Special seed experiment on STS-6 and found that seed can in fact survive a few days in low-altitude Earth orbits. The Seeds in Space Experiment for LDEF will investigate the effects on seed of exposure to space for I year.
Objectives
The specific objectives of this experiment are to evaluate the effects of space radiation on the survivability of seed stored in space under sealed and vented conditions and to determine possible resulting mutants and changes in mutation rates.
Approach
The basic concept for this experiment is to expose approximately two million seeds of many varieties to space for I year and then return them to Earth. The returned seed will be germinated along with control seed of each variety which has not been exposed in space, and the germination rates and development of the plants will be observed. The seed will be packaged in Dacron bags and stored in both sealed and vented containers mounted in a 6-in.-deep peripheral tray. Figure 61 shows photographs of the flight containers, which are painted white for thermal control. Most of the seed will be loaded into the large 12-in.-diameter sealed container to preserve pressure and sufficient moisture. This container has been constructed of aluminum with a thin dome, about 0.050 in. thick, to minimize shielding of space radiation to the top layer of seed. Layering of seed within the container provides increasing shielding to lower layers of seed. Radiation levels will be measured by thin dosimeters placed between layers of seed. Passive maximum-temperature indicators will also be placed inside the container. Another container, mounted on the bottom of the tray, will be painted black and will have a temperature range similar to the average internal temperature of the LDEF.
[148] Space-Exposed Experiment Developed for Students (SEEDS) (P0004-2)
Background
This experiment, which is closely related to the Seeds in Space Experiment (P0004-1), will offer students the opportunity to evaluate the survivability of seeds stored in the space environment and to determine possible mutants and changes in the mutation rate which may occur.
Objectives
The objectives of this experiment are to involve a very large number of students in a national project to generate interest in science and related disciplines; to offer students from the elementary through the university level an opportunity to participate in a first-hand experiment with materials flown in space; to permit active involvement in classroom experiment design, decision making, data gathering, and comparison of results; and to emphasize a multidisciplinary approach to the project involving subject areas other than science.
Approach
Approximately 11 to 12 million tomato seeds will be stored in five sealed containers mounted in a 6-in.-deep peripheral tray. (See fig. 62.) Within each sealed container, the seeds will be packaged in four Dacron bags. Passive radiation detectors will be placed inside the canisters. Figure 63 shows the large sealed containers in the tray, without the top thermal cover. After approximately a 12-month exposure to the space environment, the seed will be returned to the George W. Park Seed Co., Inc., which will provide the seed kits. In addition to flight seed, an equivalent amount of control seed will be maintained in ground storage facilities. Both sets of seeds will be evaluated postflight to determine germination rates.
After the first LDEF mission is completed, participating student groups will be provided with kits containing samples of both exposed and control seeds. The students will design and conduct their own classroom experiments. Information gathered and evaluated by the students will be made available to the public, NASA, and the Park Seed Co.
*Experiment Coordinator
